Electroacoustic transducer set



Oct. 30, 1951 J. L. HATHAWAY ET AL ELECTROACOUSTIC TRNSDUCER SET 2SHEETS- SHEET l Filed Sept. 18, 1946 Oct- 30, 1951 J. L. HATHAWAY z-:TAL

ELECTROACOUSTIC TRANSDUCER SET I2 SHEETS- SHEET 2 lll-Q72'.

Filed sept. 18, 1946 Patented Oct. 30, 1951 UNITED STATES PATENT OFFICEELECTROACOUSTIC TRANSDUCER SET Jarrett L. Hathaway, Manhasset, andWilliam Hotine, Bayville, N. Y., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application September 18, 1946,Serial N o. 697,666

(Cl. Z50-14) 6 Claims. 1

This invention relates to extremely small, compact and lightweightelectro-acoustic transducer sets capable of being worn on the person.

A specific application of this invention is in the field of vest pockettype radio receivers, although features of the invention are applicableto apparatus for aiding persons who have difficulty in hearing. When theinvention is used in connection with a radio receiver, the receivingunit may either be carried in a pocket of the wearer or strapped aboutthe waist or suspended from the shoulder of the wearer.

Hitherto, the small portable radio receiving sets designed for carriageon the person have suffered from one. or more of the followingdisadvantages: Bulkiness, excessive weight, lack of stability, andinsuilicient battery life for the required sensitivity.

The present invention overcomes these diiculties and provides anextremely small and lightweight radio receiver set capable of being wornon the person and one which possesses sufficient sensitivity forsatisfactory reception for many hours of continuous operation.

An important feature of the invention is the extremely lightweight andvery thin iiexible tubing and associated ear attachment for transferringsound from the transducer located in the housing carried on the personto the ear of the wearer. Where this feature is employed in a radioreceiver, the iiexible tubing may serve the additional purpose of anenclosure for a thin antenna wire.

Another feature of the invention is the use of a. metallic housing orcasing for the radio receiving apparatus in conjunction with a carryingbelt of such character as to increase the overall effective length ofthe antenna.

One embodiment of the invention is a radio receiver of the vest pockettype, which is contained in a housing, and comprises a battery typebuilt-in power supply, a signal rectifying and amplifying system, and anelectro-acoustic transducer. Extending from this housing and coupled tothe transducer is a thin-walled flexible tub-e conducting sound wavesfrom the transducer to a small ear plug which may be fitted into theear. Av radio antenna wire is inserted within the thin-walled exiblesound conveying tube. By way of example only, we have found that a smalldiameter Vinylite hollow tube can be used with very satisfactoryresults.

This entire unit is extremely small, compact and of lightweight and caneasily fit into a pocket of the wearer. Ii desired, the housing may beprovided with loops for enabling a carrying strap to be inserted throughthe loops, thus permittingthe set to be carried by the wearer. If astrap is employed, it is preferred that this strap include a wire orsome conducting material extending for the length of the strap andwhich, by coupling to the housing of the radio receiver, willeffectively increase the overall length of the antenna.

Another embodiment of the radio receiver is a hearing aid having acompact, small and lightweight housing containing therein a suitablemicrophone, an audio amplifier and a transducer. Here again, as in aradio receiver embodiment, there is employed a thin-walled exible tubefor conducting sound waves from the transducer to a small ear plug whichmay be tted into the ear.

A more detailed description of the invention follows in conjunction witha drawing, wherein:

Fig. l diagrammatically shows, in box form, a radio receiver of thepresent invention;

Fig. 2 is a detailed circuit diagram of the receiver of Fig. l;

Fig. 3a and 3b respectively show exploded and assembled views of theflexible sound conveying tube in association with an ear plug at one endand the telephone electro-acoustic receiver at the other end;

Fig. 4 is a perspective view of the complete vest pocket type of radioreceiver of the invention;

Fig. 5 diagrammatically shows, in box form, the invention as applied toa hearing aid type of apparatus;

Fig. 6 shows the iiexible sound conveyingI tube feature of the inventionin association with a standard telephone plug at one end and a small earplug at the other end.

Throughout the iigures of the drawing the same parts are represented bythe same reference numerals.

Referring to Fig. l of the drawing in more detail, the radio receiver ofthe invention comprises a casing represented here by a dashed rectangle2 containing therein a radio frequency vacuum tube amplier 4, a detector6 coupled to the output of the radio receiver amplifier, an audiofrequency vacuum tube amplifier 8 following the detector 6, and anelectro-acoustic transducer I coupled to the output of the audioamplifier 8. A, B and C batteries, represented diagrammatically by thebox I8, supply polarized potentials Via leads and 'I to the amplifiers dand 3, respectively. CasingI 2 is preferably made of metal although, ifdesired, a suitable molded plastic material can be used. An inputantenna I6 in the form of a Wire is connected at one end to the input ofthe radio frequency ampliner 4, and eX- tends for the major portion ofits length through the interior of a exible plastic thin-walled smalldiameter tube I2. The tube I2 has the appearance of a thin piece ofspaghetti and is coupled at one end to the transducer It and coupled atits other end to an ear plug i4. The manner in which the tube I2 may beyjoinedto thetransducer II] and the ear plug I 4 will be described inmore detail later in connection with the description of Figs. 3a and 3b.a a a I By reference to the schematic circuit diagram amplifiercomprises a pentode vacuum tube 4 having a parallel tuned input circuitLI, CI, and a parallel tuned output circuit L2, C2. A condenser C6couples the output of the radio frequency amplier 4 to a detectorcircuit `6 comprising a pair of dry rectiers XI and X2 arranged as avoltage doubler. These rectiers may be crystal detectors, or germaniumrectiiier units, silicon rectiers, or any suitable type. Although theyhave been shown as dry rectiers, it will be obvious that, if desired,they may be replaced by a vacuum tube type of rectifier, in a mannerwell known tov those skilled in the art. The output of the rectifier 6is utilized to supply the AGC voltage to the grid of tube 4 by way of aresistor R3. Rectifier 6 also furnishes an audio voltage via condenserCI to the audio amplifier 8, which is approximately double that of asingle rectifier. The output of the audio amplifier 8 is coupled to asuitable audio transformer T whose secondary winding is coupled to anelectro-acoustic trans-4 ducer I0.

Transducer unit I0 is shown as a telephone receiver having a pair ofcoils wound around the poles of a permanent magnet P and connected inseries to theY secondary winding of the audio transformer. The diaphragmis located immediately above the coils of the telephone receiver andresponds to variations in current through the coils of the transducer. Acap C having a suitable aperture centrally located therein closes thetransducer unit. This central aperture in the cap C communicates withthe interior of the thin spaghetti-like plastic tube I2. The opening atthe other end of the tube I2 communicates with the interior of the earplu-g I4, thus conveying sound waves from the transducer unit I0 throughthe interior of the plastic tube I2, to the ear of the wearer in whichthe ear plug I4 is inserted.

The antenna of the radio frequency receiver is a thin wire I6 whichextends for the major portion of its length within the plastic tube I2.Although in Figs. 1 and 2 the wire I6 appears as though the majorportion of its length were outside the plastic tube I2, it should beunderstood that these showings are merely diagrammatic and that a moreaccurate showing appears in Fig. 4, which shows the perspective View ofa radio receiver actually constructed in accordance with the invention,and tested with highly satisfactory results.

In one embodiment of the invention., suQQQSS:

4 fully tried out and practiced, the radio frequency amplifier 4, was anRCA 1L4 miniature tube, arnplier 8 was an RCA 3Q4 miniature tube, whilerectiers XI and X2 were germanium rectiiier' units. The A battery forthe filaments of the two tubes was 11/2 Volts and connected to an on-oifswitch SW. The C battery was 21/2 Volts, while the B battery was 45volts. The A battery was a small cylindrical hash-light type, while theB and C battery was a dry battery type of rectangular configuration. Theplastic spaghetti type of tube was anvinyl plastic tubingaboutthree feetlong and having an inside diameter of .060, inch. The thickness of thevinyl tubing WasLOZinch. rlhe dimensions of the receiver casing and thelocations of the elements viewable from the outside of the housing aregenerally shown in Fig. 4. For

V tuning the inputandoutput circuits of the radio Aand 3` on the top ofthe housing for enabling a screw driver to be inserted for changing thevaluesof the variable condensers CI and C2. The of Fig. 2, it will beseen that the radio frequency A antenna wire I6 had a diameter of .003inch and was especially small toe-.prevent any undue antenuaton of thesound waves passing through the tube I2 from the transducer to the earplug. "It will thus be seen that although the tube yI2 had an insidediameter of approximately'l/l of an inch, the diameter of the antennawire was considerably smaller in size so that it occupied relativelylittle space Within the tubing. a ,Y

The casing 2 was made of metal and had a rectangular shape adapted toiit into the pocket of a wearer. The on-and-oif SW switch was located atthe-top, as well as the plastic tubeI2, and the control holes I and 3.The casing 2' had a cover 2 at the bottom which could be removedquicklyl and easily for the replacement of batteries; The batteries wereslid into the bottom of theV casing 2' and required no wire connections,inasmuch as reliance was had on `contact springs withinthle' case whichengaged the battery terminals. `4 a The metallic casing 2 was alsoprovided with metallic belt loops 'I through which a belt 9 could beinserted for supporting the receiver, either from the shoulder or fromthe Waist of the wearer; The belt 9' is shown ashaving embodied thereina wire II for association with metallic snap fastener elements I3 andI5. Elements I5 are mounted on the metallic casing 2'. The metallic wireI I in the belt 9 serves to increase the overall eifective length of theantenna. If desired, the snap fastening elements I3 and I5 may beeliminated entirely, and the same result obtained by virtue ofcapacitycoupling between wire II and the metallic casing 2 when the beltis inserted through the loops 'I, 1 and worn on the wearer.v The earplug I4 was made of soft rubber and had an overall length of slightlyless than 1X2 inch and a maximum width ofv about 5A; of an inch. Theseextremely s mall dimensions enable the ear plug to be almost completelyhidden from view when inserted into the ear.

The weight of the entire receiving unit of Fig. 4, without the carryingstrap 9, was 24 oz. weight of the carrying strap was 11/2 oz. The weightof the soft rubber ear plug I4 was about An embodiment of Fig. 4 wasactually tried outy in practice in a television studio for receivingin-k structions from a small radio transmitter operating at a frequencyof 27:32 megacycles. 'Ifhe maximum output from the audio transformer T'was of the order of 50 milliwatts. n It will be understood, of course,that the invention is not iimitedft this particular freduency, or tothis' order of output since other frequencies may be used'ancl otheroutputs obtained', depending upon the types of tubes and circuitsemployed.

The manner in which the spaghetti-like plastic sound conveying tubing I2is connected to its terminal fittings is shown in detail in Figs. 3a and3b. One end of the tube I2, for example the left hand end, is pushed (bystretching it) over the tapered end of a sleeve Il whose other end isthreaded into the interior of the cap C of the telephone receiver I0.Once the end of tube I2 is pushed on the tapered end of the sleeve I l,it will remain rmly joined to this end by friction. kThe other end oftube I2, the right hand end, is similarly pushed (by stretching it) overthe tapered end of sleeve I 9 and remains fixed and is held on thesleeve by friction. If desired', a suitable cement may be used to insurea tight and permanent nt between the ends of the plastic tubing and thesleeves II and I9. The other end of sleeve I9 is provided with a flange2l which is pushed into the bore of the rubber ear plug I4 and isretained therein. It will thus be seen that the ear plug is readilyreplaceable quickly and easily, which is an important feature forsanitary reasons especially when the unit is to be used by differentpersons. While Fig. 3a shows an exploded view of the cap C, sleeve I'I,tube I2, sleeve I9, and ear plug I4, Fig. 3b shows how these nttogether. In the embodiment actually constructed and satisfactorilytried out in practice, the sleeves I 'I and I9 were made of brass,although it should be understood that, if desired, a suitable moldedplastic material may also be used.

Fig. 5 shows diagrammatically how the invention may be used inconnection with a hearing aid type of apparatus to be carried on theperson. In Fig. 5 the hearing aid is shown as a suitable housingrepresented by the rectangle 2 containing a microphone M, an audioamplier 8, an electro-acoustic transducer I0 and suitable batteries I8.If the microphone M is of the carbon type it will require a connectionto the batteries I3 in which case there will be provided a connectionshown by the dashed line 23 suitably coupled to the elements in a mannerWell known to those skilled in the art. The output of theelectroacoustic transducer I0 which will be a telephone receiver, isconveyed by a thin walled flexible plastic tube I2 to the ear plug I4.

Fig. 6 is a mechanical assemblage which shows how the plastic tubing I2and its terminal fittings can be carried as a complete plug-in typeunit.

One end of the plastic tube I2 is connected to the soft rubber ear plugI4, while the other end of the plastic tubing is connected Via sleeve l1and suitable apparatus within a housing 2' to a telephone plug 24. Thisplug 24 is adapted to be inserted into the audio output jack of anysuitable audio circuit. This audio circuit, may, for example, be theaudio output circuit of a radio receiver, or a telephone line, or astationary or portable hearing aid. The housing 2' contains in itsinterior a suitable audio transformer 25, whose terminals are connectedto the tip and sleeve of plug 24 and tc the electro-acoustic transducerunit I Il. The audio transformer 25 is a stepdown transformer andprovides a suitable change in impedance between the telephone plug endof the circuit and the earphone transducer unit I0. The sponge rubberinsert 26 serves the dual purpose of insulating the metallic casing ofthe audio transformer from the telephone plug terminals and mechanicallystabilizing the audio transformer. The telephone receiver I0 is providedwith the usual cap C having a centrally threaded aperture whichcommunicates with the interior of the sleeve I'I associated with one endof the plastic tube l2. Suitable end plugs 2'I and 28'serve to hold theelements within the housing 2.

What is claimed is:

l. In a radio receiver, an electro-acoustic transducer for producingsound waves, and means for conveying said sound waves to the ear of aperson, said means including a flexible hollow tube having one hollowend communicating with said transducenand a small hollow ear plugcornmunicating with the other end of said flexible hollow tube, and anantenna wire within said flexible hollow tube and coupled to saidreceiver.

2. A receiver having a length of spaghetti-like flexible tubing havingone hollow end in sound transfer relation to an earphone, an ear plug insound transfer relation to the other end of said flexible tubing, and athin antenna wire located in the interior of said tubing and coupled tosaid receiver.

3. In combination, a radio receiver comprising an electro-acoustictransducer, a lightweight flexible hollow tube having one hollow end insound transfer relation with said transducer, an ear plug in soundtransfer relation with the other hollow end of said flexible hollowtube, an antenna wire located within said flexible hollow tube andcoupled to the input of said radio receiver.

4. Means for conveying sound waves from an earphone having a closureprovided with a threaded aperture, comprising a relatively long hollowexible lightweight spaghetti-like thinwalled tubing, a rigid hollowsleeve substantially entirely concealed by said tubing and having athreaded end for association with said threaded aperture and a taperedend for accommodating one end of said tubing, another rigid hollowsleeve substantially entirely concealed by said tubing and having atapered end for accommodating the other end of said tubing, a softlightweight rubber-like ear plug sufciently small to be concealed withinthe ear of a person and having a bore therein and a wider diameter holealong one portion of said bore, said last rigid sleeve also having aflange for accommodation in said wider diameter hole of said ear plugfor holding said ear plug in position on said last sleeve.

5. For use with the audio output of a communication system, a telephoneplug having tip and sleeve terminals, an audio transformer coupled tosaid terminals, an earphone type of electro-acoustic transducer coupledto the output of said transformer, a thin-walled lightweight hollowilexible spaghetti-like tubing, inconspicuously small rigid hollowsleeve substantially concealed by the ends of said tubing, a lightweightear plug sufliciently small to be concealed within the ear of a personand having a bore therein for association with one of said sleeves, andmeans for linking the other sleeve to said transducer in sound transferrelation.

6. Means for conveying sound waves from an earphone having a closureprovided with a threaded aperture, comprising a relatively long hollowflexible lightweight spaghetti-like thinwalled tubing, a rigid hollowsleeve having a threaded end for association with said threaded apertureand a tapered end for accommodating one end of said tubing, anotherrigid hollow sleeve having a tapered end for 'accommodating the otherend of said tubing, a soft lightweight rubber-like ear plug suficientlysmall to be concealed within the ear of a person and having a. boretherein and a Wider diameter hole along one portion of said bore, saidlast rigid sleeve also having a flange for accommodation in said widerdiameter hole of said ear plug for holding said ear plug in position onsaid last sleeve.

` JARRETT L. I-IATHAWAY.

WILLIAM HOTINE.

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